The present invention relates to an improved method of pumping and/or transporting viscous crude oils. More particularly, the present invention relates to the introduction into crude oils in the presence of water, of an effective amount of a surfactant package that contains at least one fluorochemical surfactant to form low-viscosity oil-in-water emulsions of the heavy crudes.
Viscosity frequently limits the rate crude oil can be produced from a well. For example, in wells that are pumped by a sucker rod string, viscous drag by the crude oil on the string slows its free fall by gravity on the downstroke. On the upstroke, this drag also slows the string, decreases oil flow through the production tubing, and increases the power required to raise oil and rod string. In some instances where the oil is highly viscous, such as the Boscan field in Venezuela, the strength of the sucker rods limits the depth at which the pump can be operated. Alternatively, hydraulic pumps can be placed at the bottom of the well, but they must still overcome the high viscous drag that requires high power oil pressures and high pump horsepower.
The downhole pump usually provides the pressure required to pump the produced oil from the wellhead to surface gathering tanks. Where viscosity is high, this may require the use of extra strength wellhead equipment (packings, gaskets, heavy walled pipes and the like) to withstand the pressures required to move such viscous oil from wellhead to storage tank.
It has been proposed heretofore to reduce the viscosity of heavy crude oils prior to pumping by introducing low viscosity crude oils, white oil, kerosene or the like into the well bore to dilute or thin the produced crude. In rod pumped wells, it is common to surround the sucker rod string with an extra tubing. Low viscosity oil is pumped down this tubing so that the string is surrounded by lower viscosity oil. This added light oil then mixes with the viscous crude near the traveling valve of the pump to lighten and thin the column of crude oil being pumped from the well through the annulus formed by the inner and the production tubings of the well. Alternatively, low viscosity oil can be pumped down hollow sucker rods and the diluted crude oil produced through the annulus between the hollow rod string and the tubing.
The resulting produced crude has reduced viscosity and is more economically transported; However, these low viscosity diluents are expensive and not always available and have to be reclaimed from the diluted crude.
Another method for reading the viscosity of heavy crudes is transporting them at elevated temperatures. This method however is very expensive because the decrease in viscosity per degree temperature increase is very low. Also, the necessary heating equipment and power requirements are costly.
Other approaches that have been suggested to reduce viscosity of asphaltenic crude deposits include the use of aqueous hydrocarbon surfactant solutions to form low viscosity oil-in-water emulsion as shown in U.S. Pat. Nos. 3,943,954, 4,265,264, 4,429,554 and 4,239,052. Such emulsions generally contain a rather high percent water for example 10-40% water, which must be removed. Removal is not always easy and yields large volumes of water contaminated with oil. High treating temperatures are required for separation of water and this results in additional expenditures. Such emulsions often become unstable at a critical flow rate and invert to high viscosity water-in-oil emulsions. As a result, pumping efficiency decreases.
It is thus an object of the present invention to obviate many of the drawbacks and deficiencies associated with the various prior art technique that are presently used in the attempt to diminish the problems associated with the production and transportation of crude oils. This object is achieved by employing a surfactant package containing at least one fluorochemical surfactant which, in the presence of water, will form an oil-in-water emulsion of the viscous crude, said emulsion having a lower viscosity than the unemulsified crude.
It is a further object of the present invention to provide a crude oil in water emulsion which is stable to breakdown or inversion up to at least about 50.degree. C. containing an effective emulsion stabilizing amount of a compatible fluorochemical surfactant, or a combination of fluorochemical and hydrocarbon surfactant, such that the viscosity of such emulsion is less than about 50% of the viscosity of the crude oil.
It is a further object of the present invention to provide a method of transporting crude oil by emulsifying the oil with an aqueous solution containing an effective emulsion stabilizing amount of a compatible fluorochemical surfactant, or combination of a fluorochemical and hydrocarbon surfactant, to form an oil-in-water emulsion having a viscosity less than about 50% of the crude oil, and transporting said oil through a pipeline.
These and other objects of the present invention are apparent from the following disclosures.